Immune-Related Radiation Pneumonitis in Patients Undergoing Durvalumab Treatment After Concurrent Chemo-Proton Therapy

Abstract

Although the PACIFIC trial did not suggest that the administration of durvalumab increased the risk of radiation pneumonitis (RP) compared to placebo, the timing of durvalumab administration following concurrent chemo-radiotherapy was various and the method used to evaluate RP including interstitial pneumonia was unclear. Thus, further studies are needed to better understand the development of immune-related adverse event (irAE), in particular RP. In the present study, we performed a preliminary analysis to investigate RP after concurrent chemo-proton therapy (CCPT) followed by durvalumab.Between October 2018 and March 2020, 17 patients were administered durvalumab (mg/kg, q2w) within 14 days after CCPT (70 GyRBE/35 fractions and cisplatin (60 mg/m2) on day 1 and S-1 (w40 mg/m2 twice daily) on days 1 to 14, q4w, for up to 2 cycles). As a control, 47 patients who underwent CCPT in our previous phase II trial conducted between August 2013 and December 2017 were analyzed. These 47 patients were administered adjuvant chemotherapy (same regimen for up to 2 cycles) after CCPT. In patients suspected to have developed RP as a result of irAE, their treatment plans were compared with CT images obtained at the time of RP onset to examine the association between the dose distribution and RP.In our previous study, acute grade 2 RP within 3 months after the end of irradiation was observed in 4 patients (8.5%), and no patients developed grade 3 or higher RP. However, all occurred after completion of adjuvant chemotherapy, that is, within 2-3 months after the end of irradiation. On the other hand, 6 patients developed symptomatic grade 2 RP within 1 month of treatment among 17 patients who were administered durvalumab. Unlike CT findings of RP in the control patients, RP in 6 patients who received durvalumab was identified in the areas that received low-to-medium doses of proton irradiation and/or outside of the irradiation field, whereas the areas that received a high dose of proton irradiation exhibited little to no inflammatory response. In 3 patients who were subsequently administered steroids, CT revealed a rapid decrease in the lung volume and inflammatory response that progressed every week, in addition to traction ectasia and rapid progression of fibrosis. For the remaining 3 patients, the symptoms were mild without fever and improved only by stopping durvalmab without using steroids, and the course of CT images were similar.Administration of durvalumab soon after CCPT resulted in the unexpected or unusual course of development of RP, which was likely an irAE. Further studies are needed to better understand the cause of immune-related RP.